I have been trying to isolate the hot water to the tap in the bathroom. I have located 2 gate valves in the airing cupboard and turned them off, but the water still flows from the tap. I wondered whether the valve was simply shutting off the supply to the hot tank from the cold, but when i run off water I can hear the cold tank refilling. I think I'm gonna have to turn off at the mains and drain both tanks, but dont want to do this if I'm missing something simpler.